Thermal management in semiconductor packages is a problem common to electronic products in the computer, telecommunications, automotive and other industries. Semiconductor chips, and in particular power transistors, generate considerable heat in operation. Metal plates, or heat sinks, are frequently used in packages or assemblies to improve heat removal from the semiconductor chips. However, in most cases the chip must be electrically insulated from the heat sink. Thus a layer of dielectric material must be placed between the chip and the heat sink. Since most dielectric materials have low thermal conductivity, the efficiency of the heat sink is limited. This problem can largely be overcome by the use of beryllia as the dielectric material, since beryllia has both good dielectric properties and good thermal conductivity. However, beryllia is a highly toxic material as well as very expensive. Its use has been severely restricted in many consumer products. Therefore, there is a need for a semiconductor chip assembly which has thermal dissipation properties approaching that of assemblies containing beryllia-based dielectric layers, but which does not use toxic or excessively expensive materials.